We propose to study the mechanism of action of the experimental antitumor agents steganacin, taxol and aphidicolin. The effect of these drugs on the in vitro assembly of tubulin and on DNA synthesis will be followed. HeLa cells will be used to determine the effects of steganacin, taxol and aphidicolin on progression of the cell through the cell cycle, cellular growth, macromolecular synthesis and mitotic index.